Resin box

ABSTRACT

On a folding section of the thermoplastic sheet there is provided one or more thin-walled section, extending in a longitudinal direction of the folding section, whose minimum thickness is not less than {fraction (1/10)} and not more than ⅔ the thickness of the thermoplastic resin sheet. Thus, it is possible to provide a box in which rebound of the folding section is reduced and an operation efficiency upon setting up the box and putting goods into the box can be improved.

FIELD OF THE INVENTION

[0001] The present invention relates to a resin box, and in particularto a recursive resin box to be suitably used for a returnable box.

BACKGROUND OF THE INVENTION

[0002] Conventionally, a resin box, such as a cardboard box, a plasticbox, has been used for containers for transporting various products.

[0003] However, a cardboard box is made of paper and therefore it issensitive to water and is hardly recursive. Further, it causes a problemof paper dust, which is likely to get in the products.

[0004] To provide a replacement of such a cardboard box, JapaneseUnexamined Patent Publication No. 164933/1996 (Tokukaihei 8-164933,published on Jun. 25, 1996) and Japanese Unexamined Patent PublicationNo. 79940/2000 (Tokukai 2000-79940, published on Mar. 21, 2000) disclosea resin box, which is made of a folded resin sheet.

[0005] However, the conventional resin box made of a folded resin sheetcauses inefficiency during the fabrication of the box, as it requiressome knack to deal with its repulsion force at the folding portion. Alsothe repulsion force at the cover sections interferes the work to put inthe products in the box.

[0006] Further, in the conventional resin box made of a folded resinsheet, when the box is sealed by folding flaps (cover sections), theupper flaps for covering over the lower flaps are lifted by the lowerflaps beneath because of the compression strength in the thicknessdirection of the resin sheet. This causes deterioration of theappearance of the box after sealed, and also causes some difficultieswhen the sealing sections are sealed with tapes or the like.

[0007] Further, in the conventional resin box made of a folded resinsheet, the connection section of each side is joined with metalstitches, metal rivets, or resin pins. In this joining method, the resinsheets are joined at portions having a certain area with arbitraryintervals by using pin-shaped components

[0008] However, with this method, the resin box cannot be completelysealed, and may cause some gaps between the joining portions when aplurality of boxes is placed one on another. These gaps between thejoining portions allow dust to get in the box.

[0009] Further, the conventional resin box made of a folded resin sheetis harder than a cardboard box and therefore causes a difficulty of thefolding work.

SUMMARY OF THE INVENTION

[0010] In view of the foregoing problems, the object of the presentinvention is to provide a resin box showing reduced rebound of a foldingsection and being capable of improving operation efficiency upon settingup the box and putting goods into the box.

[0011] As a result of earnest study performed by the inventors so as tosolve the foregoing problems, they found that: as to a resin boxconstituted of a thermoplastic resin sheet, it is possible to reduce therebound of the folding section and to improve the operation efficiencyupon setting up the box and putting goods into the box by arranging asfollows. According to this, they made the present invention.

[0012] In order to achieve the foregoing object, the resin box of thepresent invention is constituted of a thermoplastic resin sheetincluding a folding section, wherein the folding section includes atleast one thin-walled section, extending in a longitudinal direction ofthe folding section, whose minimum thickness is not less than {fraction(1/10)} and not more than ⅔ the thickness of the thermoplastic resinsheet.

[0013] Further, in order to achieve the foregoing object, the resin boxof the present invention is constituted of a thermoplastic resin sheetincluding a folding section, wherein the folding section includes atleast one thin-walled section, extending in a longitudinal direction ofthe folding section, whose minimum thickness is not less than {fraction(1/10)} and not more than ⅔ the thickness of the thermoplastic resinsheet.

[0014] Note that, it is more preferable to form two or more thin-walledsections in each folding section, and in the case where two or morethin-walled sections are formed in a folded section, the thin-walledsections are formed in parallel to each other.

[0015] According to the invention, the folding section of thethermoplastic resin sheet includes a thin-walled section having athickness of not less than {fraction (1/10)} and not more than ⅔ thesheet thickness, thereby improving operation efficiency upon setting upthe box and putting goods into the box. Further, rebound of the foldingsection is reduced, thereby effectively preventing exfoliation andbreakage of the connection section joined by pasting, etc.

[0016] Therefore, it is possible to provide a resin box showing reducedrebound of the folding section and being capable of improving operationefficiency, upon setting up the box and putting goods into the box.

[0017] Further, when each folding section includes two or morethin-walled sections parallel to each other, it is possible to fold thefolding section more easily in comparison to the folding sectionincluding one thin-walled section, and to improve an upright property ofthe box.

[0018] Another object of the present invention is to provide a resin boxwhich shows reduced rebound between overlapping folded cover sections soas to improve an appearance of the box, and can be easily taped at thesealing point using a tape, etc., when the folded cover sections areoverlapped and sealed.

[0019] Further, another object of the present invention is to providesuch a resin box that: when folded covers are overlapped with each otherand are sealed, appearance of the box is improved by reducing repulsiveforce between the folding covers, and a sealing portion can be easilysealed with a tape etc.

[0020] As a result of earnest study performed by the inventors so as tosolve the foregoing problems, they found that: as to the resin boxconstituted of the thermoplastic resin sheet, by arranging the foldedcovers of the thermoplastic resin sheet as follows, the folded coversoverlapped with each other do not repel each other, and the upper foldedcover is not lifted by the lower folded cover, and the appearance of thebox is improved, and it is easier to seal the sealing portion with tapesand the like. According to this, they made the present invention.

[0021] In order to achieve the foregoing object, the resin box of thepresent invention is constituted by folding one or more thermoplasticresin sheet, wherein: the thermoplastic resin sheet is constituted oftwo or more side face sections, adjacent to each other, that areconnected via folding sections to cover sections and bottom sectionsboth of which are freely foldable, and each of the folding sectionsincludes two or more thin-walled sections parallel to each other, and inone folding section, there is provided a level difference between thecover sections adjacent to each other, and in another folding section,there is another level difference between the bottom sections adjacentto each other, the level difference being 1 to 1.2 times the thicknessof the thermoplastic resin sheet.

[0022] According to the invention, the folding sections are providedbetween the side face sections adjacent to each other and the coversections so as to have a level difference whose length is 1 to 1.2 timesthe thickness of the sheet in a depth direction of the box. For thisreason, in a case where the cover sections adjacent to each other or thebottom sections adjacent to each other are folded at an angle of 90°,there exists the level difference whose length is 1 to 1.2 times thethickness of the sheet, so that the cover sections or the bottomsections overlap with each other with less strain. As a result, it ispossible to prevent the rise of a cover sections or a bottom sectioncaused by another cover section or the bottom section. Further, it ispossible to reduce a gap between the overlapped portions, therebypreventing extraneous objects from coming into the box.

[0023] Further, there are provided two thin-walled sections parallel toeach other on a folding section, it is possible to fold the foldingsection more easily than the folding section having a single thin-walledsection thereon. Thus, it is possible to obtain not only an advantagethat an operation efficiency upon setting up the box and putting goodsinto the box is improved, but also an advantage that the rebound of thefolding section is reduced.

[0024] Therefore, it is possible to provide such a box that the reboundof the folding section is reduced and the operation efficiency uponsetting up the box and putting goods into the box can be improved.

[0025] Further, a further object of the present invention is to provideda resin box capable of enduring the repeated using, and capable ofreducing a gap between the overlapped portions so as to preventextraneous objects from coming into the box.

[0026] As a result of earnest study performed by the inventors so as tosolve the foregoing problems, they found that: a portion to which aconnection portion of the side face section is bonded extends from thefolding section on the side of the cover section to the folding sectionon the side of the bottom section, and there is no rift in bonded facesof the connection portion, so that an extraneous object such as a dustdoes not come into the box through the gap. According to this, they madethe present invention.

[0027] In order to achieve the foregoing object, the resin box of thepresent invention is constituted by folding one or more thermoplasticresin sheet, wherein: the thermoplastic resin sheet is constituted oftwo or more side face sections connected via folding sections, each ofwhich has one or more thin-walled section, to cover sections and bottomsections both of which are freely foldable, and the thermoplastic sheetincludes a connection portion connected to an opening side portion of atleast one of the side face sections adjacent to each other, and thethermoplastic resin sheet is a monolayer resin sheet constituted of afoamed layer whose expansion ratio is 1.5 to 9, or a multilayer resinsheet constituted of at least a foamed layer whose expansion ratio is1.5 to 9 and at least a non-foamed layer, and the connection portion iswelded to the side face section so that a length of the connectionportion is substantially as long as a distance between a folding sectionalong a cover section and a folding section along a bottom sectionextending from the side face section from which the cover sectionextends, and a bonded face of the connection portion extends from thefolding section along the cover section to the other folding sectionalong the bottom sections.

[0028] According to the invention, a connection portion is welded on theside face section so as to have the same length as a distance between afolding section along a cover section and a folding section along abottom section extending from the side face section from which the coversection extends.

[0029] Thus, the bonded face is successively provided from the foldingsection along the cover section to the folding section along the bottomsection. Thus, there is no rift in the bonded face on the connectionsection. Therefore, there is no possibility that dust comes through agap into the box. Further, the resin sheet itself is bonded withoutusing other adhesive, so that it is possible to efficiently recycle it.

[0030] Meanwhile, the resin sheet is a monolayer resin sheet constitutedof a foamed layer whose expansion ratio is 1.5 to 9, or a multilayerresin sheet constituted of at least one foamed layer whose expansionratio is 1.5 to 9 for each layer and at least one non-foamed layer.

[0031] In a case where the resin sheet is the monolayer resin sheetconstituted of a foamed layer whose expansion ratio is less than 1.5, orin a case where the resin sheet is the multilayer resin sheetconstituted of a non-foamed layer whose expansion ratio is less than 1.5for all layers, the resin sheet becomes heavy in case of setting up thebox. Meanwhile, the monolayer resin sheet constituted of a foamed layerwhose expansion ratio is over 9 does not bring about sufficientrigidity.

[0032] As a result, it is possible to provide the box that can endurethe repetitive usages, and has no gap in the connection section, and canprevent extraneous objects such as dust from coming into the box.

[0033] Yet another object of the present invention is to provide a resinbox capable of being easily set up and folded with improving foldingefficiency.

[0034] As a result of earnest study performed by the inventors so as tosolve the foregoing problem, they found that: as to the resin boxconstituted of the thermoplastic resin sheet, the thermoplastic resinsheet is arranged as follows, so that the operation efficiency uponsetting up the box and putting goods into the box is improved. Accordingto this, they made the present invention.

[0035] In order to achieve the foregoing object, the resin box of thepresent invention is constituted so as to be a rectangular prism byfolding at least one thermoplastic resin sheet, wherein: the at leastone thermoplastic resin sheet is constituted of two or more side facesections connected via folding sections, each of which has one or morethin-walled section, to cover sections and bottom sections both of whichare freely foldable, and the thermoplastic resin sheet is a monolayerresin sheet constituted of a foamed layer whose expansion ratio is 1.5to 9, or a multilayer resin sheet constituted of at least one foamedlayer whose expansion ratio is 1.5 to 9 and at least one non-foamedlayer, and two of the bottom sections adjacent to each other arepartially bonded to each other as one pair, and a diagonally foldingsection is provided in a substantially 45° direction from a cornersection on said one pair of the bottom sections that is externallypositioned when the bottom sections are folded, and said one pair isopposite to another pair of the bottom sections. Note that, the foamedlayer means a layer whose expansion ratio is not less than 1.5, and thenon-foamed layer includes not only an absolute non-foamed layer whoseexpansion ratio is 1, but also a slightly foamed layer whose expansionratio is not more than 1.5.

[0036] According to the invention, the thermoplastic resin sheet is amonolayer resin sheet constituted of a foamed layer whose expansionratio is 1.5 to 9, or a multilayer resin sheet constituted of at least afoamed layer whose expansion ratio is 1.5 to 9 and at least a non-foamedlayer

[0037] According to this, at least one layer is constituted of thefoamed layer, so that an end face that has been processed is notsharpened. This brings about not only the safety but also a hygienicadvantage because an extraneous object does not come into the boxthrough the end face. That is, in a thermoplastic resin sheet providedin a paper cardboard shape, the extraneous object comes into the boxthrough the end face, but in the thermoplastic resin sheet having somethickness due to the foamed layer, the extraneous object is preventedfrom coming into the box through the end face.

[0038] In the present invention, the resin box is arranged so that: thediagonally folding section is provided in a substantially 45° directionfrom a corner section on said one pair of the bottom sections that isexternally positioned when the bottom sections are folded, and said onepair is opposite to another pair of the bottom sections.

[0039] According to this, by folding the box along the diagonallyfolding sections, the box can be easily folded. Reversely, only byopening the folded resin box, the box can be obtained in athree-dimensional shape.

[0040] As a result, it is possible to provide the box capable of beingeasily set up and folded with improving the folding efficiency.

[0041] For a fuller understanding of the nature and advantages of theinvention, reference should be made to the ensuing detailed descriptiontaken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0042]FIG. 1 is a perspective diagram showing an embodiment of a resinbox in the present invention.

[0043]FIG. 2 is a development showing the resin box.

[0044]FIG. 3(a) is a sectional view showing a shape of a thin-walledsection formed in a folding section of the resin box.

[0045]FIG. 3(b) is a sectional view showing another shape of thethin-walled section formed in the folding section of the resin box.

[0046]FIG. 3(c) is a sectional view showing a further shape of thethin-walled section formed in the folding section of the resin box.

[0047]FIG. 4 is a perspective view showing the thin-walled sectionformed in the folding section of the resin box.

[0048]FIG. 5(a) is a sectional view showing a structure of a resin sheetof the resin box, which is a multilayer foamed sheet wherein a foamedlayer is sandwiched with non-foamed layers on front and back surfaces.

[0049]FIG. 5(b) is a sectional view showing a structure of the resinsheet of the resin box, which is a multilayer foamed sheet wherein thenon-foamed layer, a foamed layer with an expansion ratio of 1.5 through9, and a foamed layer with an expansion ratio of 20 through 40 aresequentially layered from below.

[0050]FIG. 5(c) is a sectional view showing a structure of the resinsheet of the resin box, which is a multilayer foamed sheet wherein thenon-foamed layer, the foamed layer with an expansion ratio of 1.5through 9, a foamed layer with a expansion ratio of approximately 30 aresequentially layered from below.

[0051]FIG. 5(d) is a sectional view showing a structure of the resinsheet of the resin box, which is a multilayer sheet wherein the foamedlayer with an expansion ratio of 1.5 through 9, the non-foamed layer,the non-foamed layer, and the foamed layer with an expansion ratio of1.5 through 9 are sequentially layered from below.

[0052]FIG. 6 is a development of another embodiment of the resin box ofthe present invention.

[0053]FIG. 7 is an end view showing an arrangement of a folding sectionof the resin box.

[0054]FIG. 8(a) is an end view showing another arrangement of thefolding section of the resin box.

[0055]FIG. 8(b) is an end view showing a further arrangement of thefolding section of the resin box.

[0056]FIG. 9 shows a side view showing a method of buckling strengthevaluation.

[0057]FIG. 10 is a perspective view showing chief members of the resinbox.

[0058]FIG. 11 is a development schematically showing the resin box.

[0059]FIG. 12(a) is a development showing one resin sheet of the resinbox.

[0060]FIG. 12(b) is a development showing the other resin sheet of theresin box.

[0061]FIG. 13 is a bottom view showing a back surface of the resin boxwhen set up.

[0062]FIG. 14(a) is a sectional view showing a locking section and alocked section on a bottom section of the resin box.

[0063]FIG. 14(b) is a sectional view showing another locking section andanother locked section on the bottom section of the resin box.

[0064]FIG. 15(a) is an exploded perspective view showing a furtherlocking section and a further locked section on the bottom section ofthe resin box.

[0065]FIG. 15(b) is a plan view showing yet another locking section onthe bottom section of the resin box.

DISCLOSURE OF INVENTION

[0066] [Embodiment 1]

[0067] The following will explain an embodiment of the present inventionwith reference to FIGS. 1 through 5.

[0068] A box 1 in the present embodiment is a box capable of beingfolded, as shown in FIG. 1. The box 1 is constituted of a resin sheet 2having a thickness of 2 mm through 10 mm. The box 1 may be constitutedof a continuous resin sheet 2, or may be composed of not less than tworesin sheets 2 which have been joined together using proper means.However, at least one resin sheet 2 constituting the box 1 is providedwith at least one folding section 3.

[0069] The folding section 3 may be a side section 3 a between adjacenttwo faces 4 which are formed of the continuous resin sheet 2, forexample. Alternatively, the folding section 3 may be a folding section 3b provided along a boundary between (1) a face 4 and (2) a connectionsection 5 (a shaded section in FIG. 2), which is a continuous section ofthe face 4, for joining the face 4 with another face 4, as shown in FIG.2.

[0070] In the box 1, the folding section 3 of the resin sheet 2 has athin-walled section 7 having a minimum thickness of not less than{fraction (1/10)} and not more than ⅔ the thickness of a general section6 of the resin sheet 2, as shown in FIGS. 3(a), 3(b), and 3(c). Thethickness of the thin-walled section 7 is more preferably not less than⅕ and not more than ½ the thickness of the general section 6 of theresin sheet 2. Namely, when the thin-walled section 7 is less than{fraction (1/10)} the thickness of the general section 6, repetition offolding easily exfoliates and breaks the thin-walled section 7. On theother hand, when the thin-walled section 7 is not less than ⅔ thethickness of the general section 6, the folding section 3 has too muchrepulsive force as described later. Note that, a groove width of thethin-walled section 7 is preferably not less than ½ the thickness of thegeneral section 6 of the resin sheet 2.

[0071] In the box 1 in the present embodiment, since the folding section3 of the resin sheet 2 is formed with the thin-walled section 7 havingthe above-described size, the repulsive force (restitutive force) isreduced at the folding section 3 of the resin sheet 2, therebyfacilitating set-up of the box 1 as well as packing goods into the box1. Further, since the repulsive force is reduced at the folding section3 of the resin sheet 2, the distortion of the box 1 itself is alsoreduced, thereby effectively preventing the breakage of the box 1 causedby the exfoliation of the connection section, etc.

[0072] The thin-walled section 7 in the folding section 3 of the resinsheet 2 may be formed in such a manner that the resin sheet 2 is heatedand compressed using proper means, for example. The thin-walled section7 is preferably formed while stretching the resin sheet 2, for achievingespecially high durability to the repetition of folding and tearing.More specifically, the thin-walled section 7 is preferably formed in thefollowing manner. The resin sheet 2 is pressed on with a pressure jig(usually a bar-shaped jig) heated at a temperature which is 5° C.through 40° C. lower than the melting point of the resin, and is thenpressured so that the pressured section of the resin sheet 2 has adesirable thickness which is not less than {fraction (1/10)} and notmore than ⅔ the initial thickness. Here, the temperature of the jigpreferably ranges from 120° C. through 150° C. when the resin sheet 2mainly includes polypropylene.

[0073] A cross-sectional shape, which is cut in a direction vertical toa longitudinal direction of the thin-walled section 7, in a vicinity ofthe thin-walled section 7 of the resin sheet 2 is not limited. Thecross-sectional shape may be a U-shape as shown in FIG. 3(a), a V-shapeas shown in FIG. 3(b), or a rectangular shape having one opening side asshown in FIG. 3(c), but usually the U-shape is preferable because it ispossible to effectively prevent stress concentration on the thin-walledsection 7. Further, in the box 1 which is formed by bonding one or moreresin sheet 2 having the thin-walled section 7, it is preferable thatthe box 1 is folded so that the thin-walled section 7 is externallypositioned, because the box 1 can stand upright more easily. Further, inview of the durability to tearing of the thin-walled section 7, athin-walled length Li of the thin-walled section 7 is preferably shorterthan a folding length L2 of the folding section 3 formed with thethin-walled section 7, as shown in FIG. 4. Further, one folding section3 is preferably formed with two or more thin-walled sections 7 which arearranged in parallel to each other. The two or more thin-walled sections7 arranged in parallel may be internally provided, or may be externallyprovided as shown in Embodiment 2 as described later.

[0074] The box 1 having the above-described arrangement can bemanufactured by properly folding the folding section 3 and joining theconnection section 5 with one or more resin sheet 2. The resin sheet 2can be joined in accordance with tacking, screwing, welding, adhesion,but preferably in accordance with the welding or the adhesion. Inaccordance with the fusion or the adhesion, the resin sheet 2 can bejoined through not only a point but also an entire face, therebyachieving high withstand load.

[0075] Further, when the resin sheet 2 is joined to the entire face inaccordance with the welding or the adhesion, it is possible to preventan extraneous object from getting into the box 1 through the connectionsection. This is highly desirable in terms of security and hygiene.Further, it is most desirable to perform the foregoing joint inaccordance with the welding because they can be strongly joined witheach other. The welding may be performed in accordance with a method inwhich the resin sheet 2 is subjected to pressure welding by heating theresin sheet 2 after being contacted with a heat plate or brought in avicinity of a pole of the heat plate. Alternatively, the fusion may beperformed in accordance with methods such as ultrasonic welding andvibration welding. The ultrasonic welding is especially desirable, sinceit is hard to damage a material around the welded section because energyis concentrated in a vicinity of the welded section.

[0076] Incidentally, the box 1 desirably has high rigidity and thinsheet thickness. In order to satisfy these demands, the general section6 of the resin sheet 2 which constitutes the box 1 in the presentembodiment preferably has a thickness of not less than 2 mm and not morethan 10 mm. When the general section 6 of the resin sheet 2 has athickness of less than 2 mm, the wall surface of the box 1 has lowrigidity, so that the box shape is hard to be retained while stored withthe contents or applied with load. On the other hand, when the resinsheet 2 has a thickness of more than 10 mm, the box 1 is too thick interms of the sheet thickness and is inferior in terms of volumeefficiency. The resin sheet 2 more preferably has a thickness of notless than 3 mm and not more than 5 mm.

[0077] Further, the above-described resin sheet 2 is constituted ofresin made mainly of thermoplastic resin such as propylene resin forexample, and is constituted of a monolayer foamed sheet having only asingle foamed layer whose expansion ratio is approximately 3, forexample, as detailed later. The resin sheet 2 preferably has a densityof not less than 0.1 g cm³ and not more than 0.6 g/cm³. Namely, when theresin sheet 2 has a density of more than 0.6 g/cm³, the resin sheet 2 istoo thick in proportion to its rigidity. On the other hand, when theresin sheet 2 has a density of less than 0.1 g/cm³, the resin sheet 2has low rigidity so that the box shape is hard to be retained and thebox 1 lacks shock resistance. Therefore, the resin sheet 2 having theabove-described density has high rigidity in proportion to its weightper unit area, and the box 1 composed of the above-described resin sheet2 has high strength in proportion to its weight.

[0078] Further, in terms of the expansion ratio, the resin sheet 2having only the single foamed layer preferably has an expansion ratio of1.5 to 9. Namely, when the resin sheet 2 has an expansion ratio of lessthan 1.5, the resin sheet 2 is of too small weight per unit area inproportion to its rigidity. On the other hand, when the resin sheet 2has an expansion ratio of more than 9, the resin sheet 2 has lowrigidity so that the box shape is hard to be retained and the box 1lacks shock resistance.

[0079] The resin sheet 2 having the low density may be a resin sheethaving a hollow structure formed with a rib and a liner, a resin sheethaving a honeycomb core hollow structure, a resin sheet having a foamedlayer, etc. Among the above-described resin sheets, the resin sheet 2having the foamed layer is preferable in view of manufacture cost of theresin sheet 2 and tractability of the resin sheet 2 when formed into thebox 1.

[0080] Further, in the present embodiment, the resin sheet 2 may bepreferably constituted of the monolayer foamed sheet having only thesingle foamed layer, as well as a multilayer foamed layer constituted ofnot less than two foamed layers, or a multilayer foamed layerconstituted of at least one foamed layer and at least one non-foamedlayer, as shown in FIGS. 5(a) through 5(d). When the multilayer foamedlayer is constituted of not less than two foamed layers, materials andexpansion ratios of the respective foamed layers may be the same, or maydiffer from one another.

[0081] As the resin sheet 2, the box 1 is preferably constituted of thefoamed sheet having both of the foamed layer and the non-foamed layer,because lightness in weight and high strength can be simultaneouslyachieved. In concrete, it is preferable to use the foamed sheetconstituted of the foamed layer whose expansion ratio is 1.5 to 9 andthe non-foamed layer, for example, because lightness in weight and highrigidity can be easily achieved. The thickness ratio of the foamed layerand the non-foamed layer can be properly determined so as to achievedesired lightness in weight and desired strength.

[0082] Here, in the present embodiment, the foamed layer is a layerwhose expansion ratio is not less than 1.5, and is approximately 2 to40, for example. On the other hand, the non-foamed layer includes aslightly foamed material whose expansion ratio is not more than 1.5, aswell as an absolutely non-foamed layer whose expansion ratio is 1.

[0083] In concrete, the resin sheet 2 shown in FIG. 5(a), for example,is constituted of (1) a foamed layer having a thickness of 2 mm through10 mm with an expansion ratio of 1.5 to 9, which is sandwiched inbetween (2) non-foamed layers respectively having a thickness of 100 μmthrough 1000 μm with an expansion ratio of less than 1.5 as the frontand back surfaces. Note that, in FIG. 5(a), one of the non-foamed layersmay be omitted. Further, the resin sheet 2 as shown in FIG. 5(b), forexample, is constituted of the non-foamed layer with an expansion ratioof less than 1.5, a foamed layer with an expansion ratio of 1.5 to 9,the non-foamed layer with an expansion ratio of less than 1.5, and afoamed layer with an expansion ratio of 20 through 40, which aresequentially layered from below. Note that, a small circle in FIG. 5(b)indicates a void. Further, as shown in FIG. 5(c), the resin sheet 2 maybe constituted of the non-foamed layer with an expansion ratio of lessthan 1.5, the foamed layer with an expansion ratio of 1.5 to 9, and thefoamed layer with an expansion ratio of approximately 30, which aresequentially layered from below. Further, as shown in FIG. 5 (d), byusing the non-foamed layer with an expansion ratio of less than 1.5 as acore material, the resin sheet 2 may be constituted of the foamed layerwith an expansion ratio of 1.5 to 9, the non-foamed layer with anexpansion ratio of less than 1.5, the non-foamed layer with an expansionratio of less than 1.5, the foamed layer with an expansion ratio of 1.5to 9, which are sequentially layered from below.

[0084] The monolayer foamed sheet can be manufactured in accordance withmethods such as atmospheric pressure heating, extrusion foaming,pressure foaming, and injection foaming. On the other hand, themultilayer foamed sheet may be manufactured in accordance with methodssuch as multilayer extrusion foaming, or may be manufactured by layeringthe respectively manufactured layers in accordance with means such asadhesion and welding.

[0085] Further, the material of the resin sheet 2 constituting the box 1in the present invention is not limited, but preferably resin includingmainly propylene resin. This is because the propylene resin(polypropylene in particular) has high performance on integral molding,weldability, heat resistance, water resistance, oil resistance, chemicalresistance, etc. The propylene resin may contain ethylene resin,elastomer, etc., as long as the characteristics of the propylene resinare not remarkably undermined.

[0086] Further, the resin sheet 2 constituting the box 1 in the presentembodiment may contain inorganic fillers such as silica, mica and talc,reinforcing materials such as glass fiber, carbon fiber, aramid fiberand ultra-high molecular weight polyethylene fiber, additives such asheat stabilizers, ultraviolet absorbers and coloring agents, ifnecessary.

[0087] The heat stabilizer may be Sumilizer BP101 (trade name,manufactured by Sumitomo Chemical Co., Ltd.), Ultranox 626 (trade name,manufactured by GE Specialty Chemicals), for example. Further, theultraviolet absorber may be Sumisorb S577 (trade name, manufactured bySumitomo Chemical Co., Ltd.), for example.

[0088] Further, the box 1 in the present embodiment is required to havefouling resistance when used as a returnable box. Generally, a box madeof resin is easily charged, and thus easily fouled by adsorbing dust andthe like. Thus, the box 1 is preferably provided with antistaticproperty. The resin sheet 2 can be provided with the antistatic propertyusing an antistatic agent.

[0089] The applicable antistatic agent may be amine compounds such asstearylethanolamine, stearyldiethanolamine, laurylamine andlauryldiethanolamine, amide compounds, ester compounds such as stearyldiethanolmonostearate and glycerin aliphatic ester, quaternary ammoniumcompounds, pyridine derivatives, and carboxylic derivatives, forexample.

[0090] The antistatic agent may be a single compound, or may be amixture of not less than two compounds. Further, the antistatic agentmay be not only low molecular weight antistatic agents as describedabove, but also polymer antistatic agents such as polyether resin andpolyamide resin, for example.

[0091] Further, among the above-described polymer antistatic agents, itis preferable to use polyether ester amide resin which is expressed inthe following general equation;

HO—[OC—R¹—NH]_(x)—(OC—(R²O)_(z)—)_(y)]_(n)—H

[0092] (where n, x, y, and z are respectively independent integralnumbers, and R¹ and R² are respectively independent alkyl group, cyclicaliphatic group, or aromatic group).

[0093] Incidentally, in a case where the box 1 is made dirty, the dirtis wiped out or washed out. The low molecular type antistatic agentmentioned as an example has high affinity with respect to water, so thatthe antistatic agent is flown with water when the box 1 is washed withwater. As a result, the box 1 loses the antistatic property. Then, thisproblem can be solved by using the polymer type antistatic agent as theantistatic agent.

[0094] In order to concretely give the antistatic property to the resinsheet 2, the following processes may be performed: the antistatic agentis kneaded into the resin before forming the resin sheet, or theantistatic agent is applied to the surface of the resin sheet 2, or afilm, having the antistatic property, that has been made in advance, isbonded to the surface of the resin sheet 2.

[0095] In the case where the antistatic agent is kneaded into the resin,the antistatic agent may be blended in an entire body of the resin sheet2, but it is preferable that, in the resin sheet 2 constituted of atleast two layers, only a layer having a surface on which the antistaticproperty is required contains the antistatic agent. For example, in acase where the antistatic property is required only on one surface ofthe resin sheet 2, the resin sheet 2 is constituted of at least twolayers, and the antistatic agent is blended only in a layer having asurface on which the antistatic property is required, so that it ispossible to efficiently achieve the desired antistatic property.Further, in a case where the antistatic property is required on bothsurfaces of the resin sheet 2, the antistatic agent is blended in bothoutermost layers in the resin sheet 2 constituted of at least threelayers, so that it is possible to efficiently achieve the desiredantistatic property.

[0096] It is possible to manufacture the layered sheet having theantistatic property in accordance with an extrusion laminating process.In a case where the polymer type antistatic agent is used to kneadingthe antistatic agent into the resin, it is preferable that a blendingamount of the antistatic agent is not less than 5 weight % with respectto the resin, and it is more preferable that the blending amount of theagent is not less than 10 weight % and not more than 20 weight %. Thisis because it is difficult to exhibit the sufficient antistatic propertyat less than 5 weight %.

[0097] As described above, according to the box 1 of the presentembodiment, it is possible to provide such box 1 that: there occurslittle rebound of the folding section 3, and the operation efficiencyupon setting up the box 1 and putting goods into the box 1 is improved,and damages caused by internal distortion is hard to occur.

[0098] Further, it is possible to preferably use the box 1 of thepresent embodiment as a returnable box since the box 1 is superior inthe durability.

[0099] [Embodiment 2]

[0100] Another embodiment of the present invention is described asfollows based on FIG. 6 through FIG. 8. Note that, the same referencesigns are given to members having the same functions as the membersshown in Embodiment 1 for convenience, and description thereof isomitted. Further, various characteristics described in Embodiment 1 areapplicable in combination with characteristics of the presentembodiment.

[0101] A box 20 of the present embodiment is made by connecting tworesin sheets 21, each of which is shown in FIG. 6, to each other. Thatis, the resin sheet 21 includes: a front/back face constituting member21 a having a cover section 8 and a bottom section 10; a side faceconstituting member 21 b; and a connection section 22. Thus, a singlesheet does not constitute four surfaces of a rectangular body as the box20, so that it is possible to miniaturize a manufacturing device and tosimplify a die.

[0102] Meanwhile, in the present embodiment, thin-walled sections 7 thatare parallel to each other are provided on a single folding section 3,and the folding section 3 is folded so that the thin-walled sections 7are externally positioned. Further, the two thin-walled sections 7 aresuch that: a thin-walled length L1 of each thin-walled section 7 isshorter than a folding length L2 of the folding section 3 having thethin-walled portions 7 thereon. Thus, both ends of each thin-walledsection 7 of the thin-walled length L1 is not thin-walled. Thus, even ina case where the box 20 is repeatedly folded in use, it is possible toprevent the folding section 3 from being torn off. Note that, althoughportions that are not thin-walled are provided on both ends of thethin-walled length L1 of each thin-walled section 7 in the presentembodiment, it is not necessary to limit the arrangement to this, forexample, it is possible to provide one or plural portions that is/arenot thin-walled at an arbitrary position of a central portion of eachthin-walled section 7.

[0103] Further, in the present embodiment, as shown in FIG. 7, the twothin-walled sections 7 are such that: supposing that a thickness of theresin sheet 21 is t, 2D that is a sum of external surface openinglengths, that is, a sum of groove widths D, is set so as to satisfy thefollowing expression.

1.4t≦2D≦1.7t  (Expression 1)

[0104] That is, in order that tugging stress is not exerted on theexternal surface as much as possible upon folding the folding section 3,it is ideal that a length of the external surface is shorter than alength of internal surface. Here, supposing that a curvature radius ofthe internal surface is X, a difference Δ between the length of theexternal surface and the length of the internal surface at the foldingsection 3 is expressed as follows. $\begin{matrix}{\Delta = {{2{{\pi \left( {X + t} \right)}/4}} - {2\pi \quad {X/4}}}} \\{= {\pi \quad {t/2}}} \\{= {1.57t}}\end{matrix}$

[0105] Thus, although it is ideal that the value is set to be 1.57t≦2D,it is found that, as described above, the setting of 1.4t≦2D≦1.7t bringsabout no problem as to body swelling in a case where the resin sheet 21having no flexibility is folded. Further, the setting of 2D≦1.7t isbased on such reason that: when 2D that is a sum of the groove widths Din the thin-walled sections 7 is too large, the resin sheet 21 tends tobe torn at the folding section 3 upon using the box 20 repeatedly. Notethat, it is preferable that the thin-walled sections 7 are set to be ina rotation angle n/4 that is the folding section 3.

[0106] Thus, it is not necessary to limit the number of the thin-walledsections 7 of the folding section 3 to two, for example, it is possibleto provide three or more grooves on the external surface as shown inFIG. 8(a). Further, as shown in FIG. 8(b), the foregoing relationship(Expression 1) is satisfied and two thin-walled sections 7 are providedon the external surface, and a single thin-walled section 7 can beprovided on the internal surface for example. Thus, it is possible toimprove an upright property of the box 20 when the box 20 is set up.

[0107] Note that, description of the following arrangements is omittedsince they are the same as in Embodiment 1: the arrangements other thanthe foregoing arrangement, for example, are (a) an arrangement in whicheach thin-walled section 7 is not less than {fraction (1/10)} and notmore than ⅔ the thickness of the sheet, (b) an arrangement in which theresin sheet 2 is a multi-layered resin sheet including at least a foamedlayer whose expansion ratio ranges from 1.5 to 9 for each layer and atleast a non-foamed layer, (c) an arrangement in which the resin sheet 2is constituted of a single-layered resin sheet including at least afoamed layer whose expansion ratio ranges from 1.5 to 9 for each layeror of a multi-layered resin sheet, and at least an outermost layercontains an antistatic agent, and (d) an arrangement in which propyleneresin is used as the resin.

[0108] As described above, in the box 20 of the present embodiment,there are provided two or more thin-walled sections 7 parallel to eachother in a longitudinal direction. Thus, it is possible to fold thefolding section 3 more easily than the folding section 3 having a singlethin-walled section 7, so that it is possible to improve the uprightproperty of the box 20.

[0109] Further, in the box 20 of the present embodiment, the thin-walledsections 7 are externally positioned, so that tugging stress exerted onthe external surface of the folding section 3 is reduced. Particularlyin a case where there are provided two or more thin-walled sections 7 onthe external surface like the present embodiment, the box 20 has moredurability with respect to repetition of folding compared with a boxhaving a single thin-walled section 7. That is, if the folding section 3is repeatedly folded at the single thin-walled section 7, a localportion is greatly damaged, so that the box 20 tends to be broken.However, in a case where two or more thin-walled section 7 are providedon the external surface, the folding section 3 is folded in a curvedmanner in terms of a cross sectional view, so that the folding section 3receives less damages compared with the folding section 3 having thesingle thin-walled section. Thus, it is possible to prevent the damagescaused by the repetition of folding, so that it is possible to providethe box 20 that is preferable in using as a returnable box.

[0110] Further, in the box 20 of the present embodiment, the two or morethin-walled sections 7 on the folding section 3 are provided so that 2D,the sum of the groove widths of the thin-walled sections 7, is 1.4 to1.7 times as thick as a thickness of the sheet.

[0111] Thus, this value is theoretically a value at which the tuggingstress exerted on the external surface of the folding section 3 isreduced, so that the stress exerted on the external surface of thefolding section 3 is reduced without fail, and rebound of the foldingsection 3 is reduced, and the body swelling of the box 20 is reduced.Thus, it is possible to secure the upright property of the box 20.

[0112] Although the present invention is detailed as follows based onexamples, a comparative example, and FIG. 9, the present invention isnot limited to them.

EXAMPLE 1

[0113] A foamed polypropylene sheet (Sumiceller (trade name) made bySumika Plastech Co. Ltd., expansion ratio: 3) having a thickness of 4 mmwas cut into a shape, shown in FIG. 2, that has been obtained bydeveloping an A type box that is 400 mm in length, 300 mm in width, and350 mm in height, as schematically shown in FIG. 1. Note that, the Atype box is referred in accordance with JIS standard.

[0114] Next, a U-shaped stick 5 mm wide that had been heated at 140° C.was pushed against a portion shown by a thick line in FIG. 2 until theminimum thickness of a sheet corresponding to the portion became 1.5 mm,so as to provide the thin-walled section 7 (hinge section) as shown inFIG. 3(a). At this time, the thin-walled section 7 was provided so thatnon-pressed portions, each of which had an approximately 1 to 3 mmlength, remained at both ends of the folding section 3 as shown in FIG.4. That is, (folding length L2−thin-walled length L1)/2=approximately 1to 3 mm.

[0115] Next, after the connection section 5 of the foamed polypropylenesheet was made to adhere to a plate heated at 250° C. for 1 minute, theconnection section 5 was connected to a receiving section 11 (barredportion in FIG. 2) of the same sheet so as to obtain the A type box.

EXAMPLE 2

[0116] A polypropylene film, having a 100 μm thickness, to which 20weight % of a polyether ester amide resin-based antistatic agent (TPAE10HP (trade name) made by Fuji Chemical Industry Co., Ltd.) has beenadded, was bonded, by using a hot melt type adhesive, to each of bothsurfaces of a foamed polypropylene sheet similar to the foamedpolypropylene sheet used in Example 1. By using the obtained layeredsheet, the A type box was obtained in the same way as in Example 1.

Comparative Example 1

[0117] An A type box was obtained in the same manner as in Example 1except that the minimum thickness of the thin-walled section 7 in thesheet was set to 3 mm.

EXAMPLE 3

[0118] A polypropylene film, having a 100 μm thickness, to which 0.5weight % of a glycerin fatty acid ester antistatic agent (Denon 2220(trade name) made by Marubishi Oil Chemical Co., Ltd.) has been added,was bonded, by using a hot melt type adhesive, to each of both surfacesof a foamed polypropylene sheet similar to the foamed polypropylenesheet used in Example 1. By using the obtained layered sheet, the A typebox was obtained in the same way as in Example 1.

[0119] (Evaluation)

[0120] The box 1 made in Examples 1 to 3 and Comparative Example 1 wasevaluated in accordance with the following method. The result is shownin Table 1.

[0121] (1) One of the cover sections 8 of the box 1 was folded bymanually pushing it over so that the side face section 9 connected tothe cover section 8 has an angle of 90° with respect to the coversection 8. After 30 seconds, the cover section 8 is released from hand.After 30 seconds passed since the cover section 8 had been released fromhand, an angle α between the cover section 8 and the side face section 9was measured. When α was not more than 135°, α was judged to bepreferable. When α is not less than 135°, α was judged not to bepreferable.

[0122] (2) Water resistance of the antistatic agent

[0123] A portion of 10 cm×10 cm was cut from the resin sheet. After theportion cut was soaked in water heated at 60° C. for 10 minutes, theportion was air-dried. The operation was performed three times. Surfaceresistivities of the sheet before and after the soaking process weremeasured. The surface resistivities were measured under the followingconditions.

[0124] Testing device: Ultra-super insulation meter SM-8210 Flat plateelectrode SME8310 both of which are made by Toa Denpa Kogyo KabushikiKaisha.

[0125] Testing environment: 23° C./50% RH

[0126] Applied voltage: 500V

[0127] Measuring operation: A voltage was applied to the foregoingportion for 10 seconds. After 1 minute passed since the application, aresistivity was measured. TABLE 1 Rebound of Surface resistance ratio(Ω) folding Before Three section soaking Once twice times Example 1Preferable 10¹⁶ 10¹⁶ 10¹⁶ 10¹⁶ Example 2 Preferable 10⁹  10⁹  10¹⁰ 10¹⁰Example 3 Preferable 10¹⁰ 10¹³ 10¹⁵ ∞ Comparative Not 10¹⁶ 10¹⁶ 10¹⁶10¹⁶ Example 1 preferable

EXAMPLES 4 and 5

[0128] Here, buckling strength evaluation that was performed by usingthe box 1 of Embodiment 1 and the box 2 of Embodiment 2 is described.

[0129] The box 1 internally provided with two thin-walled sections 7 andthe box 20 externally provided with two thin-walled sections 7 wereevaluated for the degree of the difference therebetween in bucklingstrength.

[0130] Concretely, the box 1 internally provided with two thin-walledsections 7 and the box 20 externally provided with two thin-walledsections 7 were subjected to compression test in which, as shown in FIG.9, holding plates were brought into contact with the side faces of theboxes and then load was applied downward. In this manner, the box wereevaluated for buckling strength.

[0131] Each of the boxes 1 and 2 was 325 mm in width×405 mm in depth×295mm in height. Further, DSS-2000 autograph (trade name)(made by ShimadzuCorporation Ltd.) was used as a compression tester, and compressionspeed was set to be 10 mm/min. Further, both the resin sheets 2 and 21had an expansion ratio of three times and a thickness of 4 mm. Further,a U-shaped groove was provided as the thin-walled section 7, and thedepth thereof was set to be 1.5 mm. Further, a length of both ends inthe folding section 3 except for the thin-walled section 7 was set to be2 mm. Note that, a temperature at which the stick for providing thethin-walled section 7 was heated was 140° C. upon forming thethin-walled section 7.

[0132] Table 2 shows the results of the tests performed in Example 4 inwhich the box 1 was internally provided with two thin-walled sections 7and in Example 5 in which the box 20 was externally provided with twothin-walled sections 7. TABLE 2 Example 4 Example 5 Com- Com- Bodyswelling pression Body swelling pression amount (mm) load (kg) amount(mm) load (kg) Initial stage  3.5  0 1.8  0 (upon setting up the box)Upon flexing 12.0 148 2.0  53 by 10 mm Upon flexing 22.5 293 15.0  183by 20 mm Buckling yield — 311 — 409 point

[0133] Table 2 shows the following facts.

[0134] {circle over (1)} According to the conditions of the box 1 andthe box 20 at an initial stage (upon setting up the box), the bodyswelling amount of the box 1 at the initial stage (upon setting up thebox) was 3.5 mm. On the other hand, the body swelling amount of the box20 at the initial stage (upon setting up the box) was 1.8 mm. Thus, aswelling ratio of the box 1 upon setting up the box was as large twiceas that of the box 20. That is, this means that the body swelling amountof the box 20 externally provided with two thin-walled sections 7 issmall upon setting up the box.

[0135] {circle over (2)} The body swelling amount of the box 1 when thebox flexed by 10 mm was 12.9 mm. On the other hand, the body swellingamount of the box 20 when the box flexed by 10 mm was 2.0 mm. This meansthat: merely by giving a small transverse load to the box 1, the bodyswelling amount becomes large. That is, the following result is found:in a case where a load is given from the side to the box, the bodyswelling amount that is naturally large at the side face vertical to theloading direction becomes larger.

[0136] {circle over (3)} The compression load at the buckling yieldpoint of the box 1 was 311 kg. On the other hand, the compression loadat the buckling yield point of the box 20 was 409 kg. Thus, it is foundthat the buckling strength of the box 20 was larger than that of the box1. Further, as to the buckling condition at this time, the box 1 buckledso as to externally swell. On the other hand, the box 20 buckled so asto slightly cave in.

[0137] According to the evaluation, it is found that: the box 20externally provided with two thin-walled sections 7 has a smaller bodyswelling amount at the initial stage and a larger buckling strength thanthe box 1 internally provided with two thin-walled sections 7.

[0138] [Embodiment 3]

[0139] Another embodiment of the present invention is described asfollows based on FIG. 10. Note that, the same reference signs are givento members having the same functions as the members described inEmbodiments 1 and 2, and description thereof is omitted.

[0140] The box 1 of the present embodiment, as shown in FIG. 2, is madeby folding the single thermoplastic resin sheet 2 constituted of fourside face sections 9 adjacent to each other that are connected via thefolding sections 3 to the cover section 8 and the bottom section 9 bothof which are freely foldable.

[0141] Further, it is possible to provide two thin-walled sections 7parallel to each other on the folding section 3 as shown in FIG. 10.While, the folding sections 3 are provided respectively on the side facesections 9 adjacent to each other so as to have a level difference Zbetween the cover sections 8, and the length of the level difference Zis 1 to 1.2 times the thickness of the sheet in a depth direction of thebox 1. Note that, although not shown, as to the folding sections 3connected to the bottom section 10, there is provided the leveldifference Z whose length is 1 to 1.2 times the thickness of the sheetin the depth direction of the box 1. Further, in the drawing, there isformed the level difference Z whose length is 1 to 1.2 times thethickness of the sheet in the case where the two thin-walled sections 7parallel to each other are externally provided, but the arrangement isnot necessarily limited to this. It is also possible to provide thelevel difference Z whose length is 1 to 1.2 times the thickness of thesheet in the case where two thin-walled sections 7 parallel to eachother are externally provided. Further, it is also possible to providethe level difference Z whose length is 1 to 1.2 times the thickness ofthe sheet in the case where a single thin-walled section 7 is providedon the folding section 3 regardless of whether the thin-walled section 7is provided internally or externally.

[0142] According to the foregoing arrangement, in a case where the coversections 8 adjacent to each other or the bottom sections 10 adjacent toeach other are folded at an angle of 90°, there exists the leveldifference Z whose length is 1 to 1.2 times the thickness of the sheet,so that the cover sections 8 or the bottom sections 10 overlap with eachother with less strain. As a result, it is possible to prevent the riseof the cover sections 8 or the bottom sections 10 caused by the othercover section 8 or the bottom section 10.

[0143] That is, in a case where there is not provided the leveldifference Z, the one cover section 8 or the one bottom section 10 israised by the other cover section 8 or the other bottom section 10 at aportion where the cover sections 8 or the bottom sections are overlappedwith each other, so that the one cover section 8 or the bottom section10 rises higher than the case where the level difference Z is provided,but this problem is solved by the level difference Z in the resin sheet2.

[0144] Further, in the resin sheet 2, the level difference Z causes thecover sections 8 or the bottom sections 10 not to be overlapped witheach other in a curved manner, so that it is possible to reduce a gap inthe overlapping portion. Thus, it is possible to prevent extraneousobjects from coming into the box. Note that, as to a conventionalcardboard box made of paper, paper is so flexible that the overlappingportions are flexibly united, thus bringing about no gap. Further, thelevel difference Z is 1 to 1.2 times the thickness of the sheet. Thatis, when the level difference is too large, the gap becomes large in theoverlapping portions. Thus, it is preferable that the level differenceis 1 to 1.2 times the thickness of the sheet.

[0145] Further, in a case where there are provided the two thin-walledsections 7 parallel to each other on the folding section 3, it ispossible to fold the folding section 3 more easily than the foldingsection 3 having the single thin-walled section 7 thereon.

[0146] Thus, it is possible to obtain not only an advantage that anoperation efficiency upon setting up the box and putting goods into thebox is improved, but also an advantage that the rebound of the foldingsection 3 is reduced. Thus, it is possible to provide the box 1 in whichthe rebound of the folding section 3 is reduced and the operationefficiency upon setting up the box and putting goods into the box can beimproved.

[0147] As described above, the level difference Z is provided in the box1 of the present embodiment, so that it is possible to provide the box 1in which the rebound of the folding section 3 is reduced and theoperation efficiency upon setting up the box and putting goods into thebox is improved, and damages caused by the internal distortion is hardto occur.

[0148] Further, it is possible to preferably use the box 1 of thepresent embodiment as a returnable box since the box 1 is superior inthe durability.

[0149] Note that, the box 1 of the present embodiment is made by foldingthe single resin sheet 2 constituted of four side face sections 9adjacent to each other that are connected via the folding sections 3 tothe cover section 8 and the bottom section 9. However, the box 1 is notnecessarily limited to this arrangement, but the box 1 may be arrangedby providing the side face sections 9 adjacent to each other so as to beconnected via the folding section 3 to the cover section 8 and thebottom section that are freely foldable.

[0150] Thus, it is possible to make the box 1 by folding four resinsheets 2 containing the side face sections 9 connected via the foldingsection 3 to the cover section 8 and the bottom section 10. On the otherhand, the box 1 may be arranged by joining two resin sheets 21 and 2 toeach other like the box 20 described in Embodiment 2.

[0151] Further, in the present embodiment, the box 1 is a rectangular,so that the side face section 9 exist in four surfaces, but the box 1may be provided in a polygonal manner such as a triangle plane shape inwhich three side face sections 9 exist or a pentagonal plane shape inwhich five side face sections 9 exist.

[0152] Note that, as to other arrangements, it is possible to use thecharacteristics of Embodiments 1 and 2.

[0153] [Embodiment 4]

[0154] Another embodiment of the present invention is described asfollows based on FIG. 11. Note that, the same reference signs are givento members having the same functions as the members shown in figurescorresponding to Embodiments 1 to 3, and description thereof is omitted.

[0155] In the present embodiment, as shown in FIG. 11, a connectionsection 5 as a connection portion is laminated on the side face section9 so as to have the same length as a distance from a connection point ofthe cover section 8 and the folding section 3 to a connection point ofthe bottom section 10 and the folding section 3. Concretely, not lessthan 80% area of the connection section 5 is to be bonded to the sideface section 9. Thus, it is possible to provide the box 1 that is strongwith respect to exfoliation and compression in a box shape. That is,when a bonding face 5 a occupies not less than 80% area of theconnection section 5, it is possible to substantially use the entiresurface of the connection section 5 as the bonding face 5 a.

[0156] Further, in the present invention, the bonding face 5 a issuccessively provided from the connection portion of the cover section 8and the folding section 3 to the connection portion of the bottomsection 10. Thus, there is no rift in the bonding face 5 a on theconnection section 5. Therefore, there is no possibility that dust comesthrough a gap into the box. Further, the resin sheet 2 itself is bondedwithout using other adhesive, so that it is possible to efficientlyrecycle it.

[0157] Further, as described above, the resin sheet 2 is the monolayerresin sheet constituted of a foamed layer whose expansion ratio is 1.5to 9, or the multilayer resin sheet constituted of at least a foamedlayer whose expansion ratio is 1.5 to 9 for each layer and at least asingle non-foamed layer.

[0158] That is, in a case where the resin sheet 2 is the monolayer resinsheet constituted of a foamed layer whose expansion ratio is less than1.5, or in a case where the resin sheet 2 is the multilayer resin sheetconstituted of a non-foamed layer whose expansion ratio is less than 1.5for all layers, the resin sheet 2 becomes heavy in case of setting upthe box. Meanwhile, the monolayer resin sheet constituted of a foamedlayer whose expansion ratio is over 9 does not bring about sufficientrigidity.

[0159] As a result, it is possible to provide the box 1 than can endurethe repetitive usages, and has no gap in the connection section, and canprevent extraneous objects such as dust from coming into the box.

[0160] As described above, it is possible to preferably use the box 1 ofthe present embodiment as a returnable box since the box 1 is superiorin the durability.

[0161] Note that, as to other arrangements, it is possible to use thecharacteristics of Embodiments 1 through 3.

[0162] [Embodiment 5]

[0163] The following will explain another embodiment of the presentinvention with reference to FIGS. 12 through 15. Note that, for ease ofexplanation, members having the same functions as those shown in thedrawings pertaining to the first through fourth embodiments above willbe given the same reference symbols, and explanation thereof will beomitted here.

[0164] A box 1 in the present embodiment is a box able to be folded, asshown in FIG. 1. The box 1 is constituted of a resin sheet 2 having athickness of 2 mm through 10 mm. The box 1 may be constituted of acontinuous resin sheet 2, or may be constituted of two or more resinsheets 2 which have been joined together using proper means. However, atleast one resin sheet 2 composing the box 1 is provided with at leastone folding section 3.

[0165] The folding section 3 may be a side section 3 a between adjacenttwo faces 4 which are formed with the continuous resin sheet 2, forexample. Alternatively, the folding section 3 may be a folding section 3b provided at a boundary between (1) a face 4 and (2) a connectionsection 5 (a shaded section in FIG. 2), which is a continuous section ofthe face 4, for joining the face 4 with connected sections 12 of anotherface 4, as shown in FIGS. 12(a) and 12(b).

[0166] Here, in the present embodiment, as shown in FIGS. 12(a) and12(b), the box 1 shown in FIG. 1 is completed in such a manner that thethermoplastic resin sheets 2 are joined together and folded so as to beformed into a rectangular parallelepiped shape. The thermoplastic resinsheets 2 are composed of two adjacent side sections 9 in which a freelyopenable and closable cover section 8 and a bottom section 10, or thecover section 8 and a bottom section 11 are respectively connected viathe folding section 3.

[0167] Further, in the box 1 of the present embodiment, as shown inFIGS. 12(a) and 12(b), respective portions of the two adjacent bottomsections 10 and 11 are welded via welding sections 10 a and 11 a.Further, as also shown in FIG. 13, diagonally folding sections 10 brespectively in a substantially 45° direction from corner sections 1 aare formed on a pair of bottom sections 10 which are folded to beexternally positioned among two pairs of the bottom sections 10 and thebottom sections 11 which respectively face one another.

[0168] With this, by folding the box 1 along the diagonally foldingsections 10 b, the box 1 can be easily folded. Reversely, only byopening the folded box 1, the box 1 can be obtained in athree-dimensional shape.

[0169] As a result, it is possible to provide the box 1 capable of beingeasily set up and folded with improving the folding efficiency.

[0170] Further, in the box 1 of the present embodiment, among the twopairs of the bottom sections 10 and the bottom sections 11 whichrespectively face one another, the pair of bottom sections 11 which arefolded to be internally positioned are overlapped with each other whenfolded, as shown in FIG. 14(a).

[0171] In other words, when the pair of bottom sections 11 which arefolded to be internally positioned, among the two pairs of the bottomsections 10 and the bottom sections 11 which respectively face oneanother, have the same length in their facing directions, the goods aremanaged to be put into the box 1 while the box 1 is open. However, whenthe goods are heavy to some extent, the goods may drop off through abutted section of the both bottom sections 11.

[0172] In the present embodiment, however, among the two pairs of thebottom sections 10 and the bottom sections 11 which respectively faceone another, the pair of bottom sections 11 which are folded to beinternally positioned are overlapped with each other when folded, asdescribed above. Further, one of the bottom sections 11 is longer thanthe other bottom section 11 in their facing directions.

[0173] With this, it is possible to prevent the goods from being droppedoff from the bottom, when storing somewhat heavy goods in the box 1.

[0174] Note that, the bottom section 11 preferably has the substantiallysame length as the width length of the box 1. This surely prevents thegoods from being dropped off from the bottom.

[0175] Further, in the box 1 of the present embodiment, as shown in FIG.13, among the two pairs of the bottom sections 10 and the bottomsections 11 which respectively face one another, the pair of bottomsections 11 which are folded to be internally folded are provided with(1) a bump-shaped latching section 13 on one of the overlapping bottomsections 11, and (2) a latched section 14 on the other overlappingbottom section 11, being constituted of a hole that allows thebump-shaped latching section 13 to come into the latched section 14, asshown in FIG. 14(a).

[0176] This surely prevents the goods from being dropped off from thebottom when storing somewhat heavy goods in the box 1.

[0177] Incidentally, the latching section 13 is not limited to a“fungiform” bump as shown in FIG. 14(a), but may be an L-shaped bump asshown in FIG. 14(b). Further, the latching sections 13 shown in FIGS.14(a) and 14(b) may be provided by forming a bump on the bottom section11, or by newly providing a bump with adhesion, etc. Further, as shownin FIG. 15(a), a substantially T-shaped cut 13 a is cut on one of thebottom sections 11, and the substantially T-shaped cut 13 a is folded ata right angle so as to stand upright. Then, while the T-shaped headsection is pressured so as to be bent in an arrow direction in FIG.15(a), the substantially T-shaped cut 13 a is come into the latchedsection 14 constituted of the hole on the other bottom section 11. Thepressure is then released so that the latching section 13 formed withthe substantially T-shaped cut 13 a is latched with the latched section14 on the other bottom section 11. With these steps, the latchingsection 13 can be integrally formed with the resin sheet 2.

[0178] Note that, the substantially T-shaped cut 13 a having a flat headsection is explained above, but the shape of the head section is notlimited to this. The head section may have a semicircle shape, as shownin FIG. 15(b).

[0179] Further, the respective numbers of the latching section 13 andthe latched section 14 are not limited to one, but a plurality oflatching sections 13 and a plurality of the latched sections 14 may beprovided. If the bump becomes an obstacle, the bump may be provided atthe corner section or in a vicinity of the side section.

[0180] As described above, it is possible to preferably use the box 1 ofthe present embodiment as a returnable box since the box 1 is superiorin the durability.

[0181] Further, according to the box 1 of the present embodiment, it ispossible to provide such box 1 that: there occurs little rebound of thefolding section 3, and the operation efficiency upon setting up the box1 and putting goods into the box 1 is improved, and damages caused byinternal distortion is hard to occur.

[0182] Note that, as to other arrangements, it is possible to use thecharacteristics of Embodiments 1 through 4.

[0183] As described, the resin box of the present invention has thearrangement such that the thin-walled section is made to be shorter thanthe folding section. Thus, durability in the folding can be improvedcompared to the case where the thin-walled section is made to be thesame length as that of the folding section, thus preventing the foldingsection from being easily torn and broken.

[0184] Further, the thin-walled section is externally provided in theresin box of the present invention. This reduces tensility affecting theexternal surface of the folding section. Particularly, by forming two ormore thin-walled sections on the external surface of the foldingsection, the durability in the folding can be further improved comparedto the case where only one thin-walled section is provided even when thefolding is repeated many times. More specifically, repetitive foldingwith respect to one folding section greatly damages the folding sectionand may cause breakage of the section; however, when two or morethin-walled sections are formed on the external surface, the damage ofthe folding section can be reduced for each folding section, as thefolding sections are bent rather than folded. As a result, the damagedue to the repetitive folding can be prevented, and it becomes possibleto provide a resin box can suitably be used as a returnable box.

[0185] In the resin box of the present invention, in a case where two ormore thin-walled sections are provided on the folding section, a totalwidth of the thin-walled sections is 1.4 to 1.7 times the thickness ofthe thermoplastic resin sheet.

[0186] This value can theoretically reduce the tensility affecting theexternal surface of the folding section. Thus, it certainly reduces thetensility affecting the external surface of the folding section, andreduces the repulsion force in the folding section, and also reducesbody swelling of the resin box, and further, ensures upright property ofthe resin box.

[0187] Further, in the resin box of the present invention, thethermoplastic resin sheet is a monolayer resin sheet constituted of afoamed layer whose expansion ratio is 1.5 to 9, or a multilayer resinsheet constituted of at least a foamed layer whose expansion ratio is1.5 to 9 and at least a non-foamed layer. Note that, the forming layerrefers to a layer whose forming expansion ratio is not less than 1.5.Also, the non-foamed layer includes not only absolutely non-foamed layerhaving an expansion ratio of 1, but also slightly foamed body having anexpansion ratio of less than 1.5.

[0188] In the foregoing arrangement, the thermoplastic resin sheet maybe a monolayer resin sheet, or may be a multilayer resin sheet. However,in the case of a monolayer resin sheet, its foamed layer preferably hasan expansion ratio of 1.5 to 9. Further, in the case of a multilayerresin sheet, its foamed layer preferably includes at least a foamedlayer having an expansion ratio of 1.5 to 9, and includes at least anon-foamed layer.

[0189] With this arrangement, it is possible to reduce the body swellingof the resin box, and to ensure the upright property of the resin box.Particularly, the multilayer resin sheet including at least a non-foamedlayer can further improve the upright property of the resin box, as anon-foamed layer has a higher strength than that of a foamed layer.Further, a multilayer resin sheet can improve lightness in weight andcrashproof of the box by stacking a plurality of foamed layersrespectively having different expansion ratio. This realizes twocompatible effects: lightness in weight and strength of the resin box.

[0190] Further, in the resin box of the present invention, an antistaticadditive is blended in the monolayer resin sheet or at least anoutermost layer of the multilayer resin sheet. Therefore, it reducesadsorption of dust or the like, and can keeps the resin box clean.

[0191] Further, in the resin box of the present invention, resinconstituting the thermoplastic resin sheet is propylene resin.Therefore, it is possible to provide a resin box ensuring superiorperformance in weldability, heat-resistance, water-resistance,oil-resistance, chemical resistance and the like.

[0192] Further, in the resin box of the present invention, in onefolding section, there is provided a level difference between the coversections adjacent to each other, and in an other folding section, thereis another level difference between the bottom sections adjacent to eachother, the level difference being 1 to 1.2 times the thickness of thethermoplastic resin sheet.

[0193] With these level differences of 1 to 1.2 times the thickness ofthe thermoplastic resin sheet, the adjacent cover sections and theadjacent bottom sections do not directly clash with each other when theyare folded at an angle of 90°. As a result, the cover sections and thebottom sections are not lifted by clashing with each other. Further, thegap in the portions where each cover section and each bottom sectionoverlap can be reduced, thus keeping extraneous objects out of the box.

[0194] Further, the folding section having at least two thin-walledsections is easier to fold than that having only one thin-walledsection. This ensures efficiencies during the composition of the box andthe work for putting the products in the box. Also, it reduces repulsionforce in the folding section.

[0195] With the foregoing arrangement, it is possible to provide a resinbox capable of keeping extraneous objects such as dust out of the box,and ensuring efficiencies during the composition of the box and the workfor putting the products in the box, by reducing repulsion force in thefolding section.

[0196] Further, in the resin box of the present invention, a pair of thebottom sections is internally positioned when the bottom sections arefolded, and the bottom sections of the pair are overlapped with eachother when the bottom sections are folded.

[0197] Namely, when each of the bottom sections of the pair internallypositioned when the bottom sections are folded have the same length ineach opposing direction, though it is possible to put a product whilethe box is opened, it may go through the juncture of the bottom sectionswhen the product have some weight.

[0198] However, in the present invention, a pair of the bottom sectionsis internally positioned when the bottom sections are folded, and thebottom sections of the pair are overlapped with each other when thebottom sections are folded. Thus, it is possible to prevent the producthaving some weight from being gone through the juncture of the bottomsections.

[0199] Further, in the resin box of the present invention, there isprovided a latching section in a protruding manner on one of the bottomsections overlapped with each other, and on an other bottom section,there is provided a latched section constituted of a hole that allowsthe latching section to come into the latched section.

[0200] Thus, it is possible to surely prevent the product having someweight from being gone through the juncture of the bottom sections.

[0201] The embodiments and concrete examples of implementation discussedin the foregoing detailed explanation serve solely to illustrate thetechnical details of the present invention, which should not be narrowlyinterpreted within the limits of such embodiments and concrete examples,but rather may be applied in many variations within the spirit of thepresent invention, provided such variations do not exceed the scope ofthe patent claims set forth below.

What is claimed is:
 1. A resin box constituted of a thermoplastic resinsheet including a folding section, wherein the folding section includesat least one thin-walled section, extending in a longitudinal directionof the folding section, whose minimum thickness is not less than{fraction (1/10)} and not more than ⅔ the thickness of the thermoplasticresin sheet.
 2. A resin box constituted by folding at least onethermoplastic resin sheet, wherein: the thermoplastic resin sheet isconstituted of two or more side face sections, adjacent to each other,that are connected via folding sections to cover sections and bottomsections both of which are freely foldable, and each of the foldingsections includes two or more thin-walled sections parallel to eachother, and in one folding section, there is provided a level differencebetween the cover sections adjacent to each other, and in an otherfolding section, there is another level difference between the bottomsections adjacent to each other, the level difference being 1 to 1.2times the thickness of the thermoplastic resin sheet.
 3. A resin boxconstituted by folding at least one thermoplastic resin sheet, wherein:the thermoplastic resin sheet is constituted of two or more side facesections connected via folding sections, each of which has one or morethin-walled section, to cover sections and bottom sections both of whichare freely foldable, and the thermoplastic sheet includes a connectionportion connected to an opening side portion of at least one of the sideface sections adjacent to each other, and the thermoplastic resin sheetis a monolayer resin sheet constituted of a foamed layer whose expansionratio is 1.5 to 9, or a multilayer resin sheet constituted of at leastone foamed layer whose expansion ratio is 1.5 to 9 and at least onenon-foamed layer, and the connection portion is bonded to the side facesection so that a length of the connection portion is substantially aslong as a distance between a folding section along a cover sections anda folding section along a bottom section extending from the side facesection from which the cover section extends, and a bonding face of theconnection portion extends from said one folding section on the side ofthe cover sections to said other folding section on the side of thebottom sections.
 4. The resin box as set forth in claim 3, wherein inone folding section, there is provided one level difference betweencover sections adjacent to each other, and in an other folding section,there is provided an other level difference between the bottom sectionsadjacent to each other.
 5. A resin box constituted so as to be arectangular prism by folding at least one thermoplastic resin sheet,wherein: the thermoplastic resin sheet is constituted of two or moreside face sections connected via folding sections, each of which has oneor more thin-walled section, to cover sections and bottom sections bothof which are freely foldable, and the thermoplastic resin sheet is amonolayer resin sheet constituted of a foamed layer whose expansionratio is 1.5 to 9, or a multilayer resin sheet constituted of at leastone foamed layer whose expansion ratio is 1.5 to 9 and at least onenon-foamed layer, and two of the bottom sections adjacent to each otherare partially bonded to each other as one pair, and a diagonally foldingsection is provided in a substantially 45° direction from a cornersection on said one pair of the bottom sections that is externallypositioned when the bottom sections are folded, said one pair beingopposite to another pair of the bottom sections.
 6. The resin box as setforth in claim 5, wherein said another pair of the bottom sections isinternally positioned when the bottom sections are folded, and thebottom sections of said another pair are overlapped with each other whenthe bottom sections are folded.
 7. The resin box as set forth in claim6, wherein there is provided a latching section in a protruding manneron one of the bottom sections overlapped with each other, and on another bottom section, there is provided a latched section constituted ofa hole that allows the latching section to come into the latchedsection.
 8. The resin box as set forth in claim 1, wherein thethin-walled section is shorter than the folding section.
 9. The resinbox as set forth in claim 2, wherein each of the thin-walled sections isshorter than each of the folding sections.
 10. The resin box as setforth in claim 3, wherein the thin-walled section is shorter than eachof the folding sections.
 11. The resin box as set forth in claim 1,wherein the thin-walled section is externally provided.
 12. The resinbox as set forth in claim 2, wherein each of the thin-walled sections isexternally provided.
 13. The resin box as set forth in claim 3, whereinthe thin-walled section is externally provided.
 14. The resin box as setforth in claim 1, wherein in a case where two or more thin-walledsections are provided on the folding section, a total width of thethin-walled sections is 1.4 to 1.7 times the thickness of thethermoplastic resin sheet.
 15. The resin box as set forth in claim 2,wherein the two or more thin-walled sections are provided on the foldingsection so that a total width of the thin-walled sections is 1.4 to 1.7times the thickness of the thermoplastic resin sheet.
 16. The resin boxas set forth in claim 3, wherein in a case where two or more thin-walledsections are provided on the folding section, a total width of thethin-walled sections is 1.4 to 1.7 times the thickness of thethermoplastic resin sheet.
 17. The resin box as set forth in claim 1,wherein the thermoplastic resin sheet is a monolayer resin sheetconstituted of a foamed layer whose expansion ratio is 1.5 to 9, or amultilayer resin sheet constituted of at least a foamed layer whoseexpansion ratio is 1.5 to 9 and at least one non-foamed layer.
 18. Theresin box as set forth in claim 17, wherein an antistatic agent isblended in the monolayer resin sheet or at least one outermost layer ofthe multilayer resin sheet.
 19. The resin box as set forth in claim 1,wherein resin constituting the thermoplastic resin sheet is propyleneresin.
 20. The resin box as set forth in claim 2, wherein resinconstituting the thermoplastic resin sheet is propylene resin.
 21. Theresin box as set forth in claim 3, wherein resin constituting thethermoplastic resin sheet is propylene resin.
 22. The resin box as setforth in claim 5, wherein resin constituting the thermoplastic resinsheet is propylene resin.